atomic64_test: simplify the #ifdef for atomic64_dec_if_positive() test

Introduce CONFIG_ARCH_HAS_ATOMIC64_DEC_IF_POSITIVE and use this instead
of the multitude of #if defined() checks in atomic64_test.c

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/Kconfig

diff --git a/lib/Kconfig b/lib/Kconfig
index 8269d56..72c1d46 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -340,6 +340,9 @@
 config GENERIC_ATOMIC64
        bool
 
+config ARCH_HAS_ATOMIC64_DEC_IF_POSITIVE
+	def_bool y if GENERIC_ATOMIC64
+
 config LRU_CACHE
 	tristate